The chemotactic sensory transducing receptor proteins of Eschericia Coli represent an extremely attractive system for X- ray crystallographic structural studies. These proteins (60,000 kilodaltons) span the inner membrane. In the periplasmic space, an N-terminal domain binds ligands, causing information to be transmitted across the membrane and transduced into a form which can modify the swimming behavior of these bacteria. In order to better understand how receptors interact with ligands, how information is transmitted across biological membranes and how signals are generated, crystallization of wild type and mutant forms of these molecules followed by X-ray structural studies are proposed. Preliminary results indicate that these molecules may crystallize in forms useful for structural studies. Crystalline rosettes of a large fragment of one of the E. Coli receptor/transducers have already been obtained from detergent-containing solutions using standard crystallization procedures.